Boat davit



K. L.. CAPPEL Aug. 4, 1953 BOAT DAVIT Filed Jan. .50, 1948 INVENTOR./fHZ/J L. CHP/DEL @ab MV All@ 4, 1953 K. l..` cAPPEl. 2,647,269

BOAT DAVIT v Filed Jan.V 30, 1948 3 Sheets-Sheet 2 INVENTOR KLAUS L.CAPPEL E" mi, QKM

ATTORNEYS Aug. 4, 1953 K, CAPPEL 2,647,269

A BOAT DAVIT Filed Jan. 30, 1948 'y 5 Shee'tsfSneet 3 Patented Aug. 4,1953 UNITED STATES PATENT OFFICE 8 Claims.

Existing types of davits, and more particularly those of the gravitytype, suffer from a number of disadvantages. For one thing, theircomponent parts are not integrally connected together, but performtranslatory movements with respect to each other. This, on the one hand,makes them less stable when being shaken by the rolling of the shipamong waves, while on the other hand it is the cause of considerablefrictional resistance. Furthermore, the forces applied to these davitsin order to hoist them from an outboard to an inboard position aremostly unfavorably disposed, so that ay large amount of power isunnecessarily required to accomplish this end. Their working parts arenot readily accessible, thus creating maintenance problems. 'I'heirstructure is considerably jarred by the abrupt termination of thelaunching movement.

Life boat davits operated by gravity are nevertheless favorite devicesfor launching boats in emergencies. They require a minimum of humaninterference beyond the rst simple release of boat lashings. Theiraction is not affected by failure of electrical power or destruction ofmachinery, such as are likely to occur in a disaster at sea, and theiroperation does not depend on the concerted manual effort of a number ofmen apt to act confusedly under the threat of loss of life.

To the requirement of simple and automatic operation, certain otherimportant practical elements must be added. Since a sinking Vesselusually departs from its normal upright position, the mechanicalfeatures of a davit should be such as to enable it to work even underadverse conditions of list and trim of the ship. Also, tilting of thesupporting deck should not shift any parts of the mechanism relative toeach other, creating new points of contact and thus increasingfrictionalresistance.

The effectiveness of a conventional type gravity davit may be impairedby yet another condition. Each of the pair of davit arms required tohandle a boat is controlled by a long line or rope, and in course oftime these lines will stretch. If their lengths increase by unequalamounts, and such a change goes unnoticed and uncorrected, then, uponlowering the boat, one davit arm will be somewhat ahead of, and lowerthan, the other, and the distance between both davit heads will beincreased. Since the boat suspended from these davit heads acts as aspacer tending to keep their distance constant, the davit heads will bepulled towards each other, and the davit arms be brought to bearlaterally against their respective supports, with a force that increasesas the phase difference between the davits grows with the inequality oftheir respective lines. If the diiference in stretch has reached acritical limit, such force may be sufficient, on lowering the boat, tojam the davit arm which is behind since it carries the lesser weight.rIhe davit arm which is ahead may carry a sufficiently great overload toovercome the friction at its base, caused by the pull of the attachedboat, and thus will continue to swing out alone, in which process ittears the boat from the other, jammed davit arm, upsets it andfrequently smashes it against the side of the ship. A well-constructeddavit should therefore remain unaected in its capacityto swing out, inspite of a more than inconsiderable phase difference of its twocomponent units.

By their nature, life boats and their davits must be carried on opendecks, where they are subject to the deteriorating influence of saltspray and rain. To prevent possible failure of the davit from slowdestruction, its working or contacting surfaces should be kept to aminimum, and be protected'from the weather. Moreover, since maintenanceoperations on shipboard are not likely to be too thorough, these workingsurfaces (such as pins, bearings, tracks, etc.) must be readilyaccessible, and must be capable of being serviced even by inexperiencedhands, without endangering the efficiency of the apparatus.

Owing to the constant rolling of a ship among waves, all its structures,and especially thosev on the upper decks, are subject to considerablestresses. A life boat davit must be designed to withstand deformationwhich, if carried far enough, would render its working partsineffective, to the danger of all aboard.

These requirements pose a problem which is extremely difficult ofsolution, even with compromises of ideally necessary requirements. Inthe invention here explained, I have provided a davit in which theabove-mentioned potential sources of failure have been largelyeliminated.

My invention relates to boat davits of the typ in which gravity isdepended on for moving the suspended and supported lifeboat from aninboard position of stowage in the davit arm to an outboard or launchingposition.

One object of my invention is to kobtain smoothness of the launchingoperation through employment of exclusively rotatory movements in thedavit mechanism,

Another object is the increase in safety of the launching processthrough provision of greater lateral stability of the davit arm, thusavoiding deformation of the davit structure and consequent jamming.

Another object is the avoidance of the one or several abruptlyterminated stages into which the swinging-out process is divided inprior art davits of this general type, and the substitution of a single,smooth, self-limiting movement, with a resulting avoidance of suddenstresses in the structure..

Other objects include operation of the davit even under adverseconditions of list and trim of the ship, and reduction of maintenancerequirements, with a resulting decrease in the eiectv of deteriorationand neglect on the reliability of the davit.

The invention possesses other objects4 and fea-- tures of Value, some ofwhich, with the foregoing, will be set forth in the followingdescription ofv the invention. not. limit myself to this disclosure ofspecies of my invention, as I may adopt variant embodimentsthereofwithin the scope ofthe claims.

Referring to the drawings:

Figure 1 is a side view of a preferred embodiment of my davit, supportedby the ships deck, with thestowed boat seen in front elevation;

Figure 2 isa front view of the davit of- Figure l;

Figure 3 is thersame side view as Figure 1, but with the davit arm swungout to its furthest outboard position, and the boat released from thedavit head;

Figure 4 is a skeleton diagram of the davit mechanism, showing theschematic arrangement andmovement of itscomponent parts;

Figure 5 is a modification of the embodiment of- Figure 1-, showing thedavit supported at its nboard end by a deck house, thus leaving thedeckunderneathk free for passage;

Figure 6.v shows a method of obtaining the phantom pivot center aboutwhich the davit turns, in terms of coordinate geometry.

The principle underlying my davit is illustrated schematically in Figure4, which shows essentially a simple four-bar linkage. are attachedllinks 3 and 4 by pivotally mounting them on. pins 5 and 6, respectively,to permit rotational movement thereof. A connecting link 'l is pivotedyto. the free ends of the links 3 and 4 bypins 8 and 9, respectively. Theconnecting link l at an intermediate point carries a rigidly attachedarm` l2 upwardly directed, to whose upper end a pulley i3v is journaledby a pin i4. A- linefromthe-pin M to the point of attachment of the armI 2v tothe link 'l makes an angle i6 of less than 90 degrees with` sucklink '1, while a linafrom. said. pinv 1.4 tol the pivot pin 8 makes anangle Il of about l5 degrees with the-vertical.

Near itsA upper end, they arm l2 is. provided witha lateralforkedextension i8; which carries aweight I9- which-corresponds to theweight-unf posed on the davitV by alifeboat which. acts onthemechanismin adownward. direction. A rope 2B is attached tothe weightI9, and passesoverk the pulley I3 in the direction of the pulley I5,thus` producing ay resulting force on the upper end of thearmapproximately in the directionI 2l.

The links3- and 4 are capable of rotating about the pins 5 and 6respectively, in circular paths- 22 and` 23, respectively. Theconnecting link l, and thus the arm l2- andY ail parts` rigidly attachedto: it, can be shown to rotate, with respect to the xed bar 2, about aconstantly shifting phantom pivot center which travels along the curve245 Anypointfon/ the curve 24 is determined by lt is to. be understoodthat I do To a fixed bar 2 l the intersections of the longitudinal axesof the links 3 and Ll. Thus, when the pins 8 and 9 have travelled alongthe paths 22 and 23 to some such points as 28 and 2l respectively, thepin i4, at the upper end of the arm i2, will have moved along the path28 to position 29, at which stage the instantaneous phantom pivot centerwill be at the point 3G on the path 24. This represents a typicalintermediate position of the assembly.

When the links 3 and 4l have reached their end'positions,approxim'atelyat 3 Ian'd 32 respectively, the pin I4 will be at thepoint 33.

It can be readily seen from Figure 4 that the force of the weight I9,acting downwardly under the pull of gravity, in directions 25, 25a, 25h,is always-on' the outboard side of the instantaneous phantom pivotcenter about which the link 'l andY attached' arm I2 are rotating, sothat aconstant restraining force must be exerted to balance it, as bymeans of the rope 2li. It may alsoibeseen from a comparison of the pathsof travelv Maud 28, that for the greater part of the movement ofy thelinks 3, s1.1 and l, the horizontal component of the displacement oi thephantom pivotcenter is less `than the horizontal component of travelofthe pin Hl. It is not until the links 3: and t approach aparalleldirection, such as are shown on. Figure 4, that a more rapiddisplacement of theY instantaneous phantom pivot center. takes place.

Since the only external forces actingl on the mechanism are those.exerted by the suspended weight i9. and the rope. 20, the laws of.statics demand that the resultant 2l always passes through theinstantaneous phantompivot center. As the pin 54 and with it the pointof application of the resultant 2lb, approach the outboard position. 33,both the direction and the pointof displacement of the resultant changeby increasingly smaller increments,` while the displacement of theinstantaneous phantomY pivot center is greatly accelerated. If motionwere to continue,.the phantom centerv would soonbe located on theoutboard side of the resultant 2lb, which is statically impossible. Themechanism will' therefore come to an automatic stop, as a result of theconverging` tendency of the resultant 2lb and the instant center,without any material stops being required.

At this pointl the weight I9, having travelled along a path 28a, slipsout of the forked extension I8V when the latter has been tippeddownwardly by rotation of the arm l2, and further paying out of the rope2! allows it to descend vertically,v without further movement of themechanism.

An additional feature of the mechanism isa peculiar self-damping orbraking action, which againv may. be explained with reference to theinstantaneous phantom pivot center. If the mechanism is allowed to movetoward the outboard position by rapidly paying out the rope 28', it mayovershoot the mark i. e. reach a position in which the resultant 2lbpasses to the inboard side of the instantaneous phantom pivot center,owing to the inertia of the system. When theresultant inboard turningmoment has become large enough toovercome the dynamic outboard turningmoment, the arm i2 will turn inboard again, and after a few oscillationsadopt the final outboard equilibrium position required by Statics.

In. summary, it may be affirmed that the most essential andvcharacteristic feature of this mechansmis-the behavior of itsinstantaneous phantom pivot center with respect to the point ofsuspension of the weight I9, and that if this behavior is known, allother features can either be derived from it or made to nt it for thebest possible effect. A general expression describing every phase ofthese relative movements explained above may therefore truly be said toembody the chief characteristic of the invention, and such an expression`can be set up in terms of descriptive geometry.

In Figure 6, the mechanism of Figure 4 is shown arranged in a coordinatesystem, with the X-axis passing through the fixed pins andl B,

and the Y-axis passing through one of these L w* 1 tan a tan y=X tan ay, :sin ori-ll sin 6+R sinh/+5) (M sin -sin a) :arcsm lug) \/K2+1-2K.eosa where x, y, :13' and y are measured in multiples of the link at theorigin, which link is taken as unity,

K is the distance between the pins 5 and 6, expressed in multiples ofthe link at the origin,

L is the length of the link 1, between pins 8 and 9, expressed inmultiples of the link at the origin, v

M is the length of the link 4 expressed in multiples of the link at theorigin,

a is the angle made with the X-axis by the link at the origin,

is the angle made with the X-axis by the other link, in this case thelink 4,

R is the distance between the pin I4 and the midpoint of the length L ofthe link 1, expressed in multiples of the link at the origin,

is the iangle made with the length L by the length R,

y is the angle made with the X-axis by the length L, i. e. the link 1.

All the characteristic features of the mechanism which have beendescribed above, are concisely and exa-ctly expressed in the aboveequations, and the curves 36 and 31 may easily be derived from them. Butin addition, these equations also furnish a theoretical basis for asimple method of designing the elements of the mechanism, such that anydesired range of travel of the pin I4 can be obtained.

The critical part of the curve 24 of instantaneous phantom pivotcenters, as shown on Figure 4, lies labove, the X-axis, where the rateof travel of the phantom center is accelerated,

which'has been shown above to be the cause of both the self-stopping andthe self-damping action of the mechanism. This acceleration occurs whenthe links 3 and 4 approach a parallel orientation, i. e. when the anglesa and Figure 6, are equal, and the curve 24 approaches an asymptote-cutting the X-axis about half-way between the pins 5 and 6, and makingan angle aas with such'X-axis equal to both a and and expressed by Alarge Value of aas thus means a steep curve 24 above the X-axis, and asmall value of am; indicates a curve 24 with little slope in thatregion. But `since the angle aas is also approximately equal to half theangle throughv which the links 3 and 4 turn in their passage from onelimiting position to another, it will be readily seen that the angle aasalso gives an approximate indication of the range of travel of the pinI4, which is thus dependent on the relationships between the lengths K,L, M and R.

However, an additional important consideration enters into the choice ofproportions of these lengths. The automatic actionv of the mechanismunder the iniiuence of gravity depends on the existence, at :all times,of a large moment arm of the weight 19 about the instantaneous ,phantompivot center. Now it can be shown that when the angle ass is large, thecurve 24 of phantom pivot centers billows out laterally below the X-axistosuch an extent that the moment arm is greatly diminished or evenvanishes for large values of aas, so that the mechanism, in spite vofhaving a large range of travel, would be halted in an intermediaryposition and would au; TUCOS `never reach its intendedv final positionunder the influence of gravity alone.

In proportioning the mechanism, it is therefore necessary to compromisebetween' a large range anda perpetually large moment arm, and thisl isachieved by making the inclination angle ass of the asmyptote anintermediate value, neither too large nor too small. Making use of theequations given above, and bearing in mind the relationships of thevarious elements, it then becomes a simple matter to design a mechanismkwhich will automatically travel in a predetermined range.

ln actual practice, it will be found that for the most favorable locusor curve of instantaneous phantom pivot centers, the link 1, Figure 4,should be vno larger than the distance between the fixed pivot pins 5and S, 4and the additive lengths of the rotating links 3 and 4 should beless than the distance between their points of ttachment to the fixedbar 2, by the pins 5 and i thus the resulting gravity davit may be madeto If it any shape and size of boat. The physical features of such adavit are described below, in connection'withy Figures 1, 2, 3 and 5.l

agences Securely xed to the deck 39of a vessel are the two units of thedavit structure, spaced apart a distance somewhat lessl than the. lengthof the boat 4-I which the complete Z--unit` davit is to carry. Each unitincludes a vframe 4.0 comprising apair of parallel spaced plates.Pivoted between. these plates as by the pins 42 and 43 are the. links 44and 45, whose free ends are cut out or .forked to accommodate the davitarm 46,` as shown on Figure 2. The davit arm broadens at the base, asshown on Figure l, the ends of the base being provided with journals 41and 48, which in turn are pivoted to the free ends of the links 44 andv45- by pins 49 and 5f respectively.

The davit arm is arched or otherwise shaped to accommodate the hull ofaboat 4i., as shown onFigure 1. The keel 52 of the boat issupported inthe stowed position of the lboat by a keel chock 53, While the side ofthe boat rests against the gunwale chock 54, both checks being arrangedon. the arm. 4.6 as shown on the drawings.

Means. are provided. for controlling the movement of the davit arm, andfor dropping the boat into the water from its nal position, Figure. 3,.To the releasing gear 56 in each end of the boat 4I, a 'IT-shaped hanger5'!` is attached. A. fall. 58, attached to the. top of the T-hanger,passes overv a sheave 59 journaled in the davit head,i over anothersheave .Bi journaled in the davit arm. somewhat lower down, around xedsheavesy 62 and 53 journaled in the davit frame 40, around a deck sheave64, and thence to one side of a. dual windlass drum. A similar fall E6is Vroven through the sheaves of the davit arm and frame in the otherunit of the davit arrangement, and after passing around the deck sheave'61 runs to the other side of the dualv windlass drum. The wndlass is aconventional feature of all similar types of davit arrangements and istherefore neither shown on the drawings nor described in the text.

Extending'from both sides of the davit head are a pairof sturdy cheekplates 68, whose lower parts are fashioned into hooks 89, into which tsthe crossbar of the T-hanger 5l, as shown on Figure 2. As shown onFigure 3, movement outboard and' downwardly of the davit arm, tips thehooks downwardly to allow the T-bar to slide off as the davit reachesits inclined position, at which* time the falls 58 and 66 assume theweight of the suspended boat which may then be lowered by paying out thefalls from the windlass. Raising the boat to engage the T-hanger 51against the edges of the cheek plates 58 leaves the crossbar in positionto be caught by the hooks S9 when the davit arm is swung back to itsupright position. The hooks 69 may also be made of oney piece andattached to the' underside of the davit head, or be otherwise integrallyconnected with it. In any case, they are a standard feature of allgravity davits and are not claimed as original, being indispensable toother types aswell.

In order to avoid the strain which would be placed upon the ends of theboat if it were left suspended in the stowed position, the length ofthev hanger 51 is adjusted, by means of a short chain, TI, or by othermeans,` so that the keel chock 53 will engage the keel 52 of the boatfrom underneath during the last part of the stowing operation, and willcontinue to support itin the stowed position, thus also relieving. thestrain on the hooks 59.

'The inboard. edge of the davit arm 46v may, be locked' in the stowedposition against the 'frame `4r!) by means ofv any known reliablequick-release device, not shown on the'drawings.

The choice of dimensions of the various struc.e tural parts willi dependiny part on the size of the boat which the davit is to handle. Theextent of the lateral travel of the davit head is governed by the widthof the boat, plus the required distance it is to be held away from thesidefof the ship during launching. These conditions give the approximatelength of the davit arm 46, and also the locations of its two endpositions.

Furthermore, the shipping authorities demand that a life boat davisbestill operative at a certain specific adverse list of the vessel.Therefore, the proportions of the various parts must beso adjusted thatthe suspended boat will always exert a suciently large outboard turningmoment upon thel arms in these adverse conditions. Keeping in mind theinteraction of the various parts, it is possible to fulfill all therequirements enumerated above by means of the davit mechanism heredescribed.

While I have described my invention in its preferred form and inconsiderable detail, the same is subject to alteration and modiiicationwithout departing from the underlying principles involved, and Iaccordingly do not desire to be limited in my protection to the specificdetails illustrated and described herein except as may be necessitatedby the appended claims.

I claim:

l. A gravity type davit unit for launching a boat from the deck of aship, comprising a frame for mounting on such ship, a pair oi pivot pinsmounted in parallel relationship on said frame, a pair of links, eachrotatably mounted on one of said pins, a davit arm for carrying a boat,means pivotally securing said davit arm at one end to said links, withits boat suspending end at all times outboard of the instantaneous pointof intersection of the longitudinal axes of said links, said pair oflinks constituting the only means of connection between said arm andsaid frame, and the additive lengths of said pair of links being lessthan the distance between their points of attachment to said frame, andmeans for removably suspending a boat from said arm in the inboardposition thereof.

2. A gravity type davit unit for launching a boat from the deck of aship, comprising a-frame for mounting in fixed position on such ship, apair of pivot pins mounted in parallel relationship on said frame, apair of links, each rotatably mounted on one of said pins, a davit armfor carrying a boat, means pivotally securing said davit arm at one endto said links, with its boat suspending end at all times outboard of theinstantaneous point of intersection of the longitudinal axes of saidlinks, said pair of links constituting the only means of connectionbetween said arm andsaid frame, and the additive lengths of said pair oflinks being less than the distance between their points of attachment tosaid frame, a pulley mounted in iixed position adjacent the other end ofsaid arm, means for removably suspending aboat from said arm in theinboard position thereof, and a fall running over said pulley andattached to said removable suspension means.

3. A gravity type davit unit for launching a boat from the deck of aship, comprising a rigid frame for mounting in xed position on suchship, said frame involving a pair of parallel spacedV plates, a pair ofpivot pins mounted in parallel relationship transverse of said frame, apair of links, each rotatably mounted on one of said pins, a davit armfor carrying a boat said davit arm having a broadened base, meanspivotally securing said davit arm at Said base to said pair of links,with its boat suspending end at all times outboard of the instantaneouspoint of intersection of the-longitudinal axes of said links, said pairof links constituting the only means of connection between said arm andsaid frame, and the additive lengths of said pair of links being lessthan the distance between their points of attachment to said frame, apulley mounted in fixed position adjacent the other end of said arm,means for removably suspending a boat from said arm in the inboardposition thereof, and a fall running over said pulley and attached tosaid removable suspension means.

4. A gravity type davit unit for launching a boat from the deck of aship, comprising a rigid frame mounted on such ship; a pair of pivotpins mounted in parallel relationship on said frame; a davit arm forcarrying a boat; a second pair of pivot pins mounted in parallelrelationship at one end of said davit arm; the distance between thepivot pins mounted on said arm being no greater than the distancebetween the pivot pins mounted on said frame; the length of said davitarm being no less than the distance between the pivot pins mounted onsaid frame; a link rotatably mounted at one end to one of the pivot pinson said frame and rotatably mounted at the other end to one of the pivotpins on said arm; a second link rotatably mounted at one end to theother pivot pin on said frame and rotatably mounted at the other end tothe other pivot pin on said arm; the additive lengths of said two linksbeing less than the distance between the pivot pins mounted on saidframe; pulley means mounted adjacent the other end of said arm; meansfor suspending a boat from said arm in the inboard position thereof; anda fall running over said pulley means and attached to said suspensionmeans; the relative lengths and dispositions of said links and said arm,and the distances between said pivot pins being characterized by thefact that the vertical through the center of rotation of said pulleymeans always passes to the outboard side of the instantaneous point ofintersection of the longitudinal axes of said links.

5. A gravity type davit unit for launching a boat from the deck of aship, comprising a frame mounted on such ship; a plurality of pivot pinsmounted in parallel relationship on said frame; a plurality of links;each of said pins having one of said links rotatably mounted upon itadjacent one end of said link; a davit arm for carrying a boat; aplurality of pivot pins mounted in parallel relationship adjacent oneend of said arm; each of said pivot pins mounted on said arm having theother end of one of said links rotatably mounted upon it; and means forsuspending a boat from said davit arm in the inboard position thereof,the relative motions of said arm and said links being characterized bythe fact that in the extreme inboard and extreme outboard positions ofsaid arm the pivot pins mounted on said arm are on opposite sides of theline joining the centers of the pivot pins mounted on said frame.

6. A gravity type davit unit for launching a boat from the deck of aship, comprising a frame mounted on such ship; a plurality of Divot pinsmounted in parallel relationship on said frame; a plurality of links;each of said pins having one of said links rotatably mounted upon itadjacent one end of said link; a davit arm for carrying a boat; aplurality of pivot pins mounted in parallel relationship adjacent oneend of said arm; each of said pivot pins mounted on said arm having theother end of one of said links r rotatably mounted upon it; said linksconstituting the only means of connection between said frame and saidarm; and means for suspending a boat from said davit arm in the inboardposition thereof, the relative motions of said arm and said links beingcharacterized by the fact that in the extreme inboard and extremeoutboard positions of said arm the pivot pins mounted on said arm are onopposite sides of the line joining the centers of the pivot pins mountedon said frame.

7. A gravity type davit including a pair of davit units, each unitcomprising a frame for mounting on a ship, a pair of pivot pins mountedin parallel relationship on said frame, a pair of links, each rotatablymounted on one of said pins, a davit arm of greater length than eitherof said links, means pivotably securing said davit arm at one end tosaid links with its boat suspending end at all times outboard of theinstantaneous point of intersection of the longitudinal axes of saidlinks, and means for removably suspending a boat from said arms in theinboard position thereof.

8. A gravity type davit including a pair of davit units, each unitcomprising a frame for mounting on a ship, a pair of pivot pins mountedin parallel relationship on said frame, a pair of links, each rotatablymounted on one of said pins, said pair of pivot pins constituting theonly means of supporting said links on said frame, a davit arm ofgreater length than either of said links, means pivotally securing saiddavit arm at one end to said links, with its boat suspending end at alltimes outboard of the instantaneous point of intersection of thelongitudinal axes of said links, said pair of links constituting theonly means of support for said arm on said frame, and the additivelengths of said links being less than the distance between their pointsof attachment to said frame, and means for removably suspending a boatfrom said arms in the inboard position thereof.

KLAUS L. CAPPEL.

References Cited in the file of this patent FOREIGN PATENTS NumberCountry Date 477,012 France June 21, 1915 481,587 France Sept. 28, 1916504,479 Great Britain Apr. 26, 1939

